Bacterial and archaeal globins - a revised perspective

Area of Science:

• Microbiology
• Bioinformatics
• Structural Biology

Background:

• Globins are heme-containing proteins involved in oxygen transport and sensing.
• Previous studies have identified diverse globin types across different life forms.
• The evolutionary history and functional diversity of bacterial and archaeal globins remain incompletely understood.

Purpose of the Study:

• To conduct a comprehensive bioinformatics survey of putative globins in bacterial and archaeal genomes.
• To classify identified globins into families and subfamilies based on structural and sequence features.
• To explore the distribution, combinations, and potential functions of these globins in prokaryotes.

Main Methods:

• Bioinformatic analysis of over 2200 bacterial and 140 archaeal genomes.
• Classification of globins into M, S, and T families based on the myoglobin fold.
• Identification of globin subfamilies, including flavohemoglobins (FHbs), single domain globins (SDgbs), globin-coupled sensors (GCSs), protoglobins (Pgbs), sensor single domain globins (SSDgbs), and truncated hemoglobins (TrHbs).

Main Results:

• Over half of bacterial and approximately one-fifth of archaeal genomes encode globins.
• Globins were classified into three main families: M (myoglobin-like), S (sensor), and T (truncated).
• Eight globin subfamilies were identified, with 83 out of 147 possible combinations observed across genomes. The FHb+TrHb2 combination was most frequent.
• Smallest globin-bearing genomes were found in the SAR11 clade and Aquificae. Methylacidiphilum infernorum possessed all three globin families.
• Potential functions include nitric oxide detoxification and oxygen sensing.

Conclusions:

• Bacterial and archaeal genomes harbor a significant diversity of globin genes.
• The classification into M, S, and T families provides a framework for understanding globin evolution and function.
• While nitric oxide detoxification and oxygen sensing are proposed functions, in vivo evidence remains limited for most identified globins.